My thoughts were that they were actually a transexual, as there's several hints given towards this conclusion - but I've not seen anyone discussing this elsewhere.
Shogakukan collected its chapters in fifteen volumes, released from July 30, 2003 to April 28, 2011.
Compare that to another scene involving a churning horny sand monster, and the distinction is pretty clear.
In reality, she is actually the woman who killed Nanako in a car accident, the event that also caused his amnesia.
Some Japanese shows and movies have subtitles available in Japanese, which can be really helpful for beginners.
You never know what you're gonna get in these films, because anything goes.